Device Tree • Re: Trouble reading from a MCP23017

Code:

#include <stdio.h>#include <fcntl.h>#include <unistd.h>#include <stdlib.h>#include <stdint.h>#include <sys/stat.h>#include <sys/types.h>#include <sys/ioctl.h>#include <linux/i2c-dev.h>#define MCP0_ADDR 0x20#define MCP1_ADDR 0x21#define IODIRA 0x00#define IODIRB 0x01#define GPIOA  0x12#define GPIOB  0x13#define INPUT 0xFFstatic const char *device = "/dev/i2c-1";uint8_t buffer[2]; int mcp0, mcp1, mcp2;int mcp_init(void) {   // Initialize 1st MCP23017 with 0x20 address:   mcp0 = open(device, O_RDWR);   ioctl(mcp0, I2C_SLAVE, MCP0_ADDR);   // Initialize 2nd MCP23017 with 0x21 address:   mcp1 = open(device, O_RDWR);   ioctl(mcp1, I2C_SLAVE, MCP1_ADDR);   // Chip 0   buffer[0] = IODIRA;   buffer[1] = INPUT;   write(mcp0, buffer, 2) ;  // set IODIRA to all inputs   buffer[0] = IODIRB;   buffer[1] = INPUT;   write(mcp0, buffer, 2) ;  // set IODIRB to all inputs   // Chip 1   buffer[0] = IODIRA;   buffer[1] = INPUT;   write(mcp1, buffer, 2) ;  // set IODIRA to all inputs   buffer[0] = IODIRB;   buffer[1] = INPUT;   write(mcp1, buffer, 2) ;  // set IODIRB to all inputs}int main(void) {   // Main loop:    // Initialize the chips:   mcp_init();   printf("init\n");   sleep(1);   while(1)   {      buffer[0] = GPIOA;      if (read(mcp0, buffer, 1) == 1)      {         printf("Good read MCP0A %02X ", buffer[0]);      }      else      {         printf("Bad read MCP0 ");      }            buffer[0] = GPIOB;      if (read(mcp0, buffer, 1) == 1)      {         printf("MCP0B %02X ", buffer[0]);      }      else      {         printf("Bad read MCP0B ");      }            buffer[0] = GPIOA;      if (read(mcp1, buffer, 1) == 1)      {         printf("MCP1A %02X %02X ", buffer[0]);      }      else      {         printf("Bad read MCP1A ");      }      buffer[0] = GPIOB;      if (read(mcp1, buffer, 1) == 1)      {         printf("MCP1B %02X ", buffer[0]);      }      else      {         printf("Bad read MCP1B ");      }      printf("\n");      sleep(1);   }  return 0 ;}